1. Field of the Invention
The present invention relates generally to nuclear fuel pellet handling techniques and, more particularly, is concerned with an apparatus for vacuum transfer (gripping and lifting) of multiple fuel pellets standing on end in a random arrangement.
2. Description of the Prior Art
Arrays of nuclear fuel pellets in a green, or unsintered, state are typically loaded into rectangular containers, or boats, from stainless steel shelfs, or trays, in preparation for placing the fuel pellets in a sintering furnace. Heretofore, at a transfer station where the pellets are loaded from the trays into the boats, a vacuum transfer apparatus has been used. The vacuum transfer apparatus includes a overhead vacuum hood with an open bottom and a plate closing the hood bottom. The plate has an array of small openings with small vacuum cups attached thereto. Each vacuum cup is flexible, of conical shape, seated in one of the holes through the plate, and has a central bore therethrough for communicating a vacuum pulled in the interior of the hood with the surface of a given one pellet contacted by the vacuum cup.
The construction of the above-described prior art vacuum transfer apparatus has drawbacks in terms of the high degree of precision required in the placement of the fuel pellets to be gripped and lifted and the lack of versatility of the apparatus. For instance, each vacuum cup on the plate must rest precisely on the top of each pellet before the suction or vacuum is applied to ensure that a vacuum will be formed with the pellet end surface. The shallow concavity present in each end surface of the pellet further complicates the problem of effective application of the vacuum to the end surface. Because of the precision required in applying each vacuum cup to a pellet end surface, the vacuum cup size must match pellet diameter size, which can range from 0.38 to 0.42 inch. As a result, the plate on the hood must be changed for different pellet sizes, as the spacing between the pellets also varies according to diameter size.
These changes require considerable time. Also, an inventory of vacuum cup plates must be maintained. Further, because the array or pattern of the vacuum cups on the plate is fixed, the pellets must be precisely arrayed on the tray so as to match the fixed array of the vacuum cups.
Consequently, a need exists for a vacuum transfer apparatus construction which will avoid these drawbacks without introducing new ones in their place.